1. Field of the Invention
The invention relates in general to elevator systems of the traction type, and more specifically to arrangements for increasing the traction efficency and reducing wear in such systems.
2. Description of the Prior Art
In elevator systems of the traction type, steel ropes or cables pass over a drive or traction sheave, with the ends of the cables on one side of the drive sheave being connected to the elevator car, and with the ends on the other side being connected to the counterweight. The physical size and rating of the traction machine connected to rotate the drive sheave is determined by the traction efficiency of the system, which is responsive to the ratio of the rope and/or sheave life to the required tractive effort.
Tractive effort has been increased by constructing the cable grooves of the drive sheave with relatively wide undercuts, such as about 3/8 inch (9.5 mm.) for 1/2 inch (12.7 mm.) rope, in order to pinch the rope and/or an additional wrap around the drive sheave is provided in combination with an additional secondary or idler sheave. A wide undercut in the cable groove severely pinches the rope, adversely affecting its useful operating life, and the double wrap idler sheave arrangement doubles the load on the shaft and bearings of the drive sheave in addition to adversely affecting useful operating life of the rope due to the additional bends therein. These structures also limit the operating pressure (radial force per inch) in the cable grooves, which usually requires that the diameter of the drive sheave be increased and/or a larger number of ropes are required, resulting in uneconomical low speed machines.
My U.S. Pat. No. 3,838, 752, which is assigned to the same assignee as the present application, discloses arrangements for increasing traction efficiency of a traction elevator system by utilizing a synthetic traction lubricant which increases the coefficient of friction between the ropes and the cable grooves of the sheave, while extending the useful operating life of the ropes due to the lubrication thereof. In addition to the advantages provided by the synthetic lubricants disclosed in my patent, it would be desirable to provide a new and improved mechanical arrangement, for further improving the tractive effort of a traction elevator system, which mechanical arrangement may be used with the synthetic lubricants, if desired.